Mechanism of Nano-Structuring Manipulation of the Crystallization Temperature of Superlattice-like [Ge8Sb92/Ge]3 Phase-Change Films.

Qingqian Qiu,Yifeng Hu,Pengzhi Wu,Jiwei Zhai,Tianshu Lai

doi:10.3390/nano11010020

Qingqian Qiu, Yifeng Hu + Show 3 more

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https://doi.org/10.3390/nano11010020

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Journal: Nanomaterials	Publication Date: Dec 24, 2020
Citations: 5	License type: CC BY 4.0

Affiliation: Tongji University, Sun Yat-sen University

Abstract

Superlattice-like (SLL) phase-change film is considered to be a promising phase-change material because it provides more controllabilities for the optimization of multiple performances of phase-change films. However, the mechanism by which SLL structure affects the properties of phase-change films is not well-understood. Here, four SLL phase-change films [Ge8Sb92(15 nm)/Ge (x nm)]3 with different x are fabricated. Their behaviors of crystallization are investigated by measuring sheet resistance and coherent phonon spectroscopy, which show that the crystallization temperature (TC) of these films increases anomalously with x, rather than decreases as the interfacial effects model predicted. A new stress effect is proposed to explain the anomalous increase in TC with x. Raman spectroscopy reveals that Raman shifts of all phonon modes in SLL films deviate from their respective standard Raman shifts in stress-free crystalline films, confirming the presence of stress in SLL films. It is also shown that tensile and compressive stresses exist in Ge and Ge8Sb92 layers, respectively, which agrees with the lattice mismatch between the Ge and Ge8Sb92 constituent layers. It is also found that the stress reduces with increasing x. Such a thickness dependence of stress can be used to explain the increase in crystallization temperature of four SLL films with x according to stress-enhanced crystallization. Our results reveal a new mechanism to affect the crystallization behaviors of SLL phase-change films besides interfacial effect. Stress and interfacial effects actually coexist and compete in SLL films, which can be used to explain the reported anomalous change in crystallization temperature with the film thickness and cycle number of periods in SLL phase-change films.

Highlights

In recent years, phase-change memory (PCM) has been recognized as one of the promising generations of memory devices because PCM may have many advantages over current static random access memory (SRAM), dynamic random access memory (DRAM), and flash memory devices as well as optical DVD-ReWritable disc memory, including high speed, good thermal stability, non-volatility, low power consumption, good scalability from micro- to nano-meter cell size, and good compatibility with Si-based Complementary Metal Oxide Semiconductor (CMOS) techniques [1,2,3,4]
Two kinds of measurements reveal the anomalous increase in the crystallization temperature of SLL phase-change films with x
The lattice mismatches certainly result in the occurrence of stress in SLL films—a long-range effect

Summary

Introduction

Phase-change memory (PCM) has been recognized as one of the promising generations of memory devices because PCM may have many advantages over current static random access memory (SRAM), dynamic random access memory (DRAM), and flash memory devices as well as optical DVD-ReWritable disc memory, including high speed, good thermal stability, non-volatility, low power consumption, good scalability from micro- to nano-meter cell size, and good compatibility with Si-based Complementary Metal Oxide Semiconductor (CMOS) techniques [1,2,3,4]. Doping phase-change materials with single elements or compounds has been used extensively to enhance both the thermal stability [8,9,10,11,12] and resistance of the crystalline state [11,12], and to reduce the crystallization time of phasechange materials. It was very difficult for doping alone to fulfill all advantages of phase-change memory or to optimize all properties of phase-change materials [8,9,10,11,12,13]

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